Estonian Journal of Earth Sciences, 2008, 57, 3, 125–134 doi:10.3176/earth.2008.3.01

Subsidence hazards connected to quarrying activities in a karst area: the case of the sinkhole event (, NW )

Sabrina Bonettoa, Adriano Fioruccib, Mauro Fornaroa, and Bartolomeo Vignab a University of Torino, 35 via Valperga Caluso, 10125 Torino, Italy; [email protected], [email protected] b Politecnico di Torino, 24 C. so Duca degli Abruzzi, 10129 Torino, Italy; [email protected], [email protected]

Received 28 December 2007

Abstract. Gypsum is an important raw material for constructions and other industrial sectors. In Piedmont (NW Italy), main gypsum bodies are located in the Monferrato area, where large open pits and underground quarries are present. The gypsum- bearing formation outcropping in this area shows typical geological, structural, and hydrogeological features, which affect the quarrying and the related interaction with natural phenomena, human activities, and land use. In particular, gypsum karst has considerable influence on mining operations, as well as mining operations can produce strong impact on gypsum karst. In Monferrato, a specific case of interaction between the quarrying activity and geological, hydrogeological, and territorial setting is represented by the event of water inrush that happened in the Moncalvo underground quarry in association with the development of a surface sinkhole phenomenon.

Key words: gypsum, quarries, karst, inrush, sinkhole, NW Italy.

INTRODUCTION activities. The investigated area corresponds to the Monferrato domain (Piedmont, NW Italy), belonging to Quarrying activity has increased in the last few years the Tertiary Piedmont Basin, where all active gypsum due to the high demand for natural raw materials in quarries of Piedmont are located (Fig. 1). different industrial sectors. An inadequate management of the exploitation of natural resources has frequently been responsible for environmental and safety problems. METHODS OF GYPSUM EXPLOITATION According to both the geomechanical behaviour of the AND MINING TECHNOLOGIES material and the geohydrological features of deposits and vulnerability of the exploited sites, proper planning According to the local geological, structural, and morpho- schemes and management are necessary in order to logical setting, the exploitation activity is nowadays set ensure the adequate use of raw materials and meeting the up in open pit and underground hillside quarries. Open criteria of the environmental sustainability and safety of pit quarrying is applied if burdens have a relatively quarrying. small thickness with respect to that of the ore body. This study focuses on gypsum, which is an important After soil removal, the exploitation is developed inside raw material particularly for the industrial buildings the ore body with a single face or bench wall succession. sector. Because of its wide distribution, gypsum has been Usually, gypsum is removed from the top to the bottom used for thousands of years in many geographical areas of the deposit, leaving single benches 10–12 m high and of the world: as building material (in Knossos Palace in with a 70° dip, in order to guarantee the stability of the Crete), dimensional stone (in Muslim Architecture), raw face. Bench configuration can be accomplished by means material to produce mortars (in Cheops Pyramid and of horizontal or vertical slices. The horizontal descending stone ships), decoration plasters and base for polychrome slices method allows realization of the consequential paintings (in Nefertari Tomb), Gypsum exploitation has environmental rehabilitation simultaneously with mining grown in the last few years due to the high demand on works and ensures safer working conditions because the domestic and international market and new quarries risks of rock downfalls and collapses at the face are have been opened (Bonetto et al. 2005; Bonetto 2006). lower. However, some problems should be considered in gypsum The equipment and mining methods depend on the quarries, related to karst phenomena, water circulation, features of the ore body and mineral resource. Mining and geomechanical features, which influence mining equipment is mainly represented by pneumatic drilling

125 Estonian Journal of Earth Sciences, 2008, 57, 3, 125–134

Fig. 1. Structural sketch map of northwestern Italy. IL, Insubric Line; SVZ, Sestri- Zone; VVL, Villavernia–Varzi Line; PTF, Padan thrust front; TH, Torino Hill domain; AM, Alto Monferrato Domain; BG, Borbera Grue domain; M1, Messinian mélange; M2, “normal” Messinian succession (Dela Pierre et al. 2002). hammers, truck excavators and blast, with hydraulic dimensions of 5–7 m in width and 6–8 m in height, breakers without blasting, and, in particular cases, just whereas squared pillars are normally 6 m side. In order rippers or surface miners. Depending on distances, muck to guarantee safety and healthy working conditions, removal is conducted by means of dozers, mechanical emergency exits and a proper airway have to be planned wheel shovels, and dumpers for the transport. on the basis of the number and type of the mining Open pit quarries have some advantages, such as the equipment. integral exploitation of the ore body, high mechanization Sometimes open pit quarries originate from digging and the large size of mining equipment with the reduction up previous underground quarry structures, by means of of powder in blasting operations. Otherwise, mining uncovering works. works are affected by meteorological conditions because rainfalls stop quarrying activity; gypsum is often marked by lower quality material and environmental impact GYPSUM DEPOSITS IN THE MONFERRATO should be strong and evident. AREA (PIEDMONT, NW ITALY): On the other hand, underground mining meets the GEOLOGICAL AND HYDROGEOLOGICAL requirements of land conservation, has low environmental FEATURES RELATED TO QUARRYING impact, and the quality of natural raw material is good. The method is traditionally developed with drill and blast In Piedmont (NW Italy), large open pits and underground techniques, by creating rooms and abandoning pillars, gypsum quarries are concentrated in the Monferrato arranged as a chess board; recently a new technology, area where the main gypsum bodies are located. In continuous mining machinery, has been introduced (road particular, gypsum belongs to the Gessoso Solfifera header). Several superimposed levels are also created. Formation (also named Complesso Caotico di Valle Versa Each of them is organized with parallel development in the new geological cartography; see Dela Pierre et al. drifts, following the dip of the gypsum beds, from 2003), which crops out in a discontinuous manner from which the exploitation drifts reach out with a steady Moncucco to (about 35 km). Main deposits are angle, following the strike of gypsum strata (Fornaro et located in the municipalities of Moncucco, Castelnuovo al. 1996). Different mining levels are reachable through Don Bosco, , , Montiglio, , a helical ramp, which can be used by big lorries. , Moncalvo, Calliano, Grana, Montemagno, In order to ensure void stability and safety conditions, Vignale, and Altavilla. pillars and slabs have to be whole and able to stand on The Gessoso Solfifera Formation consists of thick their own: rooms are usually stable, with maximum beds of coarse- and fine-grained gypsum (up to 15 m each)

126 S. Bonetto et al.: Subsidence hazards in a karst area with marly interbeds, a few decimetres up to 2–3 m thick (Fig. 2). Locally, thin evaporitic limestone beds are present at the bottom of the succession, whereas marls and clays with gypsum levels (from some decimetres to some metres thick) occur on the top. The evaporitic succession is organized in up to 150 m thick irregular bodies extending for a few kilometres and being locally intersected by karst phenomena. In places, a few system faults occur in gypsum deposits, which sometimes have a marly filling. The geological, structural, hydrogeological, and geo- technical features of the gypsum-bearing formation influence the quarrying and determine the interaction between natural phenomena, human activities, and land use. According to both the geotechnical and geo- Fig. 3. Exploitation scheme for underground gypsum quarries: mechanical behaviour of the material and the geo- drifts are organized on regular superimposed sublevels. They hydrological features of the deposits, a correct design in have to be completely mined in gypsum, leaving a coaxial gypsum square or rib pillars. the planning as well as management stages of the quarry has to be provided. With regard to gypsum bodies, main geological aspects are represented by marly interlayers, marly fillings of discontinuities, the presence of karst supporting structures (steel ribs and nets, spritz beton), circuits, and the thickness and geotechnical features of which require continuous monitoring. Moreover, covers and bordering formations. the marly and clayey deposits (layers or cave and As a consequence, the stability of the quarry structures fault refillings) represent a waste in the quarrying and the geometrical parameters of the sill, crown, and production. rib pillars are strictly connected with the drifting depth, Due to high solubility of gypsum in fluent water, it thickness and kind of cappings, and geostructural setting is possible to recognize evidences of Quaternary karst of the ore body. Refillings and layers of marl can activity (caves, potholes, pipes) in most of the open pits compromise the stability conditions both in open pit and (Moncalvo, Montiglio, Cocconato, Murisengo, Moncucco) underground quarries. In open pit quarries, bench height and underground quarries (Moncalvo, Moncucco). The must be reduced; in underground quarries, drifts have permeability of gypsum depends, principally, on the to be completely mined in gypsum, leaving gypsum sill presence and features of discontinuities (opening and pillars thick enough to avoid collapses and raises (Fig. 3). frequency), whereas primary permeability is very low. In case of the cut-off of marl layers, reinforcement As a matter of fact, stratigraphical and structural dis- of the mining walls has to be provided by means of continuities represent possible ways for groundwater flow, causing an increase in dissolution processes and development of karst morphology. Consequently, gypsum karst has considerable influence on mining operations, as well as mining operations can produce strong impact on gypsum karst, particularly when water pumping is involved and quarrying interferes with the local hydrogeological setting (increase in flow velocities and dissolution rate, lowering of the water table, breaching of artesian confinement, draining of surface flows, extension of drawdown cones). Risks are particularly connected to the presence of large empty karst caves or caves filled with marly-clayey deposits or water; in those cases, water exerts dangerous pressure on mining. In Monferrato, a specific case of interaction between quarrying activity and geological, hydrogeological, and territorial setting was revealed in the water inrush into the Fig. 2. Gypsum strata with marly interbeds, belonging to the Moncalvo underground quarry. The event was associated Messianian Gessoso Solfifera Formation. with the development of a surface sinkhole.

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INTERACTION BETWEEN EXPLOITATION by means of continuous mining machinery represented ACTIVITY AND NATURAL PHENOMENA: by the road header, instead of the traditional blasting THE WATER INRUSH INTO THE techniques (Fig. 6). MONCALVO GYPSUM QUARRY Due to the technical features of the road header, development and exploitation drifts in the production The Moncalvo gypsum quarry has been working since panels do not intersect one other orthogonally as in a 1993 and actually consists of 12 km of drifts, which are blasting exploitation, but take a “lozenge pattern”. For organized on three regular superimposed sublevels, that reason, rooms and square pillars have been replaced connected by a helical ramp, between 170 and 113 m by rooms and rib pillars with a smooth and regular a.s.l. An older open pit quarry is also present near the profile of the mining walls (Fig. 7), protecting, at the underground quarry (Fig. 4). same time, the surrounding gypsum from the typical A survey campaign with three drillings (besides the damages of blasting methods in favour of general stability already existing 24 drillings) and piezometers was (Fornaro et al. 1996, 2000). Drifts are straight, have organized in order to plan the mining operation and a low dip (< 10°) and an adequate radius of curvature investigate the geological and hydrogeological features in order to guarantee the maximum yield of the road of the gypsum body. The body consists of regular coarse- header. and fine-grained 10–15 m thick gypsum strata, which are separated by marly layers, a few decimetres up to 2 m thick. The burden of the exploited gypsum deposit is represented by a succession of marls with thin inter- beds of gypsum and clayey-marly loose material. In the open pit quarry the stratigraphical succession and evidences of Quaternary karst phenomena (caves, potholes, pipes) are better recognizable (Fig. 5). In particular, four gypsum strata have been recognized, placed in succession from the top to the bottom of the ore body. One stratum consists of fine-grained and three strata are composed of coarse-grained gypsum. Starting from the top of the deposit, sublevels of the quarry are developed in correspondence with the three upper gypsum strata: the first sublevel is set out in the single fine- grained gypsum layer, whereas the other two sublevels take up the coarse-grained gypsum strata. Because of low mechanical resistance and abrasiveness of gypsum and regularity of the ore body, the quarry is exploited Fig. 5. Karst evidences at the surface in the open pit quarry of Moncalvo.

Fig. 4. The quarry area of Moncalvo: the open pit and the underground quarry are marked by circles. Fig. 6. The road header used in the Moncalvo gypsum quarry.

128 S. Bonetto et al.: Subsidence hazards in a karst area

Fig. 8. Area of level 1 flooded by the water inrush. The scheme shows the characteristic lozenge pattern applied due to the use of road header mining machinery.

Fig. 7. Profile of the drifts mined with the road header.

From the beginning of the exploitation, the whole gypsum body was sound and massive; just occasionally a few discontinuities and dry relict weakly developed karst features (in particular in the SW zone of the quarry, between 150 and 190 m a.s.l.) were detected. In correspondence with some discontinuities, local water inflows, with a limited and constant discharge (< 1 l/s) occurred at 129–176 m a.s.l., mainly in the SE area of the quarry. The two existing piezometers recorded other water inflows, with higher discharge and 1–3 bar pressure. Repeated measurements showed a quite stable water table at about 170 m a.s.l. In the morning of 15 February 2005, during excavation Fig. 9. Sinkhole at the surface, originating from the Moncalvo works at level 1, leading to level 2 (134 m a.s.l.), the underground gypsum quarry. road header hit a fracture at the mining face with a water inflow of low discharge, but high hydraulic pressure. As a precaution, the workers were immediately moved to the The inrush event occurred because of the cut-off of a higher drifts. At 6 p.m. an inrush event suddenly took karst cave during mining works, which made the wall of place with water discharge of some cubic metres. During rock between the drift and the natural cave too thin to the night, a large amount of water (about 60 000 m3) and resist the water pressure behind it. In particular, it has terrigenous marly sediments rushed into the quarrying been noted that the point of inrush was located at the drift, submerging the road header and flooding lower bottom of the drift, near to the marly layer separating drifts of level 1 up to an elevation of 139 m a.s.l. (Fig. 8). two different gypsum layers. After drainage, the drift of As a consequence of the inrush event, between 10 p.m. the inrush was surveyed: a large amount of terrigenous and midnight of the same day, a collapse funnel with sediments lay in front of the mining face covering the a minimum depth of 10 m and maximum diameter of road header. All these sediments were removed and the about 20 m was formed at the surface (sinkhole) at the road header was dismantled and taken away. A hole with NE border of the quarry area (Bonetto & Fornaro 2005; the diameter of about 1 m was discovered, connecting Fig. 9). the quarrying drift with a natural karst cave (Fig. 10). In the next few days, the water flow showed a dis- During 2005 and 2006, water discharge from karst charge of about 20 l/s in connection with the hydraulic circuit decreased and became stable at about 8–10 l/s. pressure of about 4 bar in the karst circuits before the Water inflows from fractures near the point of inrush event. A pump was installed at level 1 in order to reduce (already present before the event) were reduced to a and stabilize the water level in the quarry, which went dripping. The pumping was continued and the water down progressively to 135.5 m a.s.l. level settled at 134.7 m a.s.l.

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Fig. 11. Scheme of the studied karst circuits after the lowering of water of the inrush event. Fig. 10. Hole in the mining face at the point of the inrush.

SURVEYING METHODOLOGIES AND THE FIRST RESULTS

On account of the water lowering in the drift, the karst cave behind the mining face was scoured. A large room (a few hundred cubic metres) and three main inter- connected conduits were discovered, oriented respectively towards SO, NW, and NNW (Fig. 11). The southwestward conduit is about 10 m long and leads to a siphon from which main water inflow originates. The second pipe extends for about 200 m to the northwest along the marly layer between the second and third strata of coarse-grained gypsum and has a circular diameter of about 5–7 m (Fig. 12). It is located just below the quarry drifts: the distance between the roof of the cave Fig. 12. Example of pipes and rooms discovered during the and the floor of the drift varies from 6 to 13 m. The dome speleological surveying. roof of the cave suggests that it was a conduit with a full load and gives assurance about the stability of the voids. The third conduit is about 100 m long and passes which allowed the reconstruction of local geology and through the three coarse-grained gypsum layers with an overburden thickness. Borings were equipped with irregular section. Actually it is completely dry and ends at piezometers, and an automatic rain gauge (with hourly the sinkhole where a funnel-shaped deposit of terrigenous measurements) was installed to monitor the groundwater sediments and woody material coming from the surface table in relation to rainfalls and mine water pumping. is present. During scouring activities, in the large room Water inflows in the quarry (VC, VP3, VBA, and just behind the mining face, two main water inflows VBB) and in the karst conduits (VS, VB, and VR) were were recognized: the main one came from the siphon of collected and analysed seasonally by means of chemical- the southwestward conduit, whereas the other one was physical laboratory tests. Moreover, a weir, equipped connected to a discontinuity and showed a discharge of with a digital data-logger, was installed close to the a few litres per second. point of the inrush in order to measure the level, the Besides safety restoring operations, surface and sub- temperature, and the electrical conductivity of the water surface investigations were carried out to understand coming from the karst system (Fig. 13). better groundwater circulation, triggering mechanisms For over one year, the discharge values measured at of the sinkhole event, origin and quality of water inflows. the weir were nearly the same (about 10 l/s), with a Subsurface exploration was conducted by means of three small increase of about 1–2 l/s during major rainfalls borings (SN1, SN2, S24) and the geophysical method, (February 2006, May 2006, September 2006, May 2007; using electrical and seismic refraction tomography, Fig. 14). Similarly, even if data collected have shown

130 S. Bonetto et al.: Subsidence hazards in a karst area

Fig. 13. Distribution scheme of the monitoring points (VC, VB, VR, VS, VP, VP3, VBA, VBB: water inflows; SO–S11, S13–S17, S21–S23: old drillings; SN1, SN2, S24: new drillings with piezometers).

Fig. 14. Trend of the inrush discharge monitored at the weir.

131 Estonian Journal of Earth Sciences, 2008, 57, 3, 125–134 a strong connection between water pumping in the quarry moves principally along fractures and stratigraphical and piezometric measurements, no relation has been discontinuities, such as the contacts between gypsum observed between the levels of the groundwater table strata and marl layers. As a matter of fact, one of the in piezometers and rainfall; all values seem to be main scoured pipes develops at the bottom of the second independent of each other and different from the value coarse-grained gypsum stratum, just along the contact directly monitored in the drifts (SN1 = 214 m a.s.l.; SN2 with the underlying marly layer. Similar evidences were = 184.3 m a.s.l.; S4 = 225 m a.s.l. at the end of the revealed by drillings: the presence of small karst caves summer 2006; Fig. 14). Also temperature values recorded at the contact between the Messinian evaporitic formation in the weir are almost constant with a gentle fluctuation (Gessoso Solfifera Formation) and the older Tortonian of 0.5 °C, without regard to discharge variations. marls (Sant’Agata Fossile Formation).

LOCAL HYDROGEOLOGICAL SETTING OF EXPLOITATION PLANNING AND THE MONCALVO QUARRY AREA MANAGEMENT IN CASE OF ACTIVE GYPSUM KARST Chemical and physical analyses of the water inflows sampled in the quarry drifts (VC, VP3, and VBA) show The monitoring programme and investigations are still sulphate-calcic water type. In particular, a different in progress to define better the hydrogeological structure quality has been noted for the water coming from the of the gypsum rock mass and identify the feeding source siphon (VS) and for that in fractures (VB, VR). The of the gypsum karst. Useful data can be furnished by VS-sample shows a lower mineralization (low concent- means of direct and indirect methodologies, as for + + + – 2– rations of Mg , Na , K , Cl , and SO4 ) and a higher example drillings, geophysical surveys, speleological value of nitrates, which are not present in VB and VR. surveys, tracer tests, census and monitoring of springs In order to identify better different inflows in the karst (natural or formed during mining works). In particular, system, the redox-potential (Eh) has been measured: boreholes have to be provided with piezometers in order generally, it is positive for the water coming from the to monitor the water table depth in different sectors of surface and negative for slow water that has no the quarry area. connection with it. The inflows VB, VBA, and VBB, as Drillings and electrical and seismic refraction tomo- well as the water coming from external piezometers, graphy should help to identify the geological features of show a negative Eh, whereas VP3 and VC samples have the deposit, the overburden thickness, and the presence positive values (Amalberto et al. 2006). of natural caves. They can be carried out both on the Consequently, the gypsum rock mass is probably surface and quarry sublevels in order to guarantee a better characterized by both a slow flow of the water coming resolution and establish more precisely the location of from the surface along main discontinuities with a geological structures and voids. high nitrate-bearing ratio and positive redox-potential The quantity and pressure of groundwater have to (samples in piezometers, VP3 and VC) and a slow be strictly defined, as well as the presence of empty or flow of the water trapped in the fracture net of the refilled natural caves, which should represent a risk in gypsum body and in the surrounding marls with a low terms of quarry stability and general safety. Therefore, nitrate-bearing ratio and negative redox potential, locally during exploitation works, it is necessary to renew geo- intersected by quarry drifts (VBA, VBB) and karst logical and structural surveys in order to update project circuit (VB). Full load karst pipes, nowadays still data. In particular, drillings of different directions have partially active, seem to be the main collector that to be performed periodically to prevent unexpected and drains various water inflows. dangerous inrush events; in case of water inflow into the The independent behaviour of the groundwater table hole, a manometer and a safety valve have to be in closely spaced piezometers suggests that discontinuities installed to check the variation of hydrostatic pressure are not interconnected and confirm the heterogeneity and avoid uncontrolled discharge of water. of the water flow in the gypsum rock mass. The low Pumping can contribute to a progressive lowering of connection of the groundwater table with rainfalls, the the water table and allow the exploitation activity to be consequent stable discharge of the water inflows, and carried on and deepened by means of new sublevels the slow rate of water circulation in the rock mass are below the present ones. Pumping discharge has to be probably due to the low permeability and limited out- usually similar to the water inflows coming from the croppings of gypsum, besides the presence of poorly karst system to avoid inconvenient lack of balance in permeable thick marl and clay covers. Therefore, water the natural system and has to be checked by pumping

132 S. Bonetto et al.: Subsidence hazards in a karst area tests. In order to monitor natural and induced strains in to the popularization of the scientific knowledge about the gypsum body, particularly in case of water table the inrush event. fluctuations, it is convenient to make periodically pinch measurements with bend or optical distometers and install pressure cells and transducers (electric or vibrating wire) at the mining wall. By processing the collected data, the REFERENCES stress distribution in the ore body should be rebuilt and represented in a proper 3D-model in order to verify Amalberto, S., Banzato, C., Civita, M., Fiorucci, A. & Vigna, B. general stability conditions on the basis of the mechanical 2006. L’inrush nella cava di gesso di Moncalvo (AT). behaviour of gypsum and overburden. On this subject, In Proceedings of the GEAM Conference “Le cave in situ tests can be carried out during drillings and in sotterraneo” – 20–21 giugno 2006, Torino, pp. 107– samples can be collected for laboratory tests to define 112. useful geotechnical parameters (cohesion, friction angle, Bonetto, S. 2006. Il gesso: da risorsa economica a patrimonio specific weight, deformation modulus, elastic modulus, culturale del Monferrato. Aggiornamento tecnico, compressive strength, shear strength). metodologie operative e ipotesi di riuso dei siti di cava dimessi. Doctorate Thesis, Politecnico di Torino, 447 pp. Bonetto, S. & Fornaro, M. 2005. Subsidence events related to DISCUSSION natural conditions and gypsum quarrying activity in the Monferrato area (Piedmont, NW Italy). In Proceedings

of MAEGS14 – 14th Meeting of the Association of A detailed study of the local geological and hydro- European Geological Societies, Torino, 19–23 September geological features is strictly necessary for a proper 2005, pp. 61–62. management and future planning of exploitation activities. Bonetto, S., Dino, G. A. & Fornaro, M. 2005. Guide lines for Surveying and speleological activity in the case of the the quarrying exploitation of messinian gypsum deposit: Moncalvo quarry contributed to the discovery of the the case of the Monferrato area (Piedmont, NW Italy). presence of karst conduits with full load, probably fed In Proceedings of the First International Conference by lateral and/or basal inflows, which represents the on the Geology of Tethys, 12–14 November, 2005, Cairo first such case in Italy. In Europe, just a few similar University, pp. 209–217. karst systems are present, for example in the Permian Dela Pierre, F., Piana, F. & Clari, P. 2002. Il Monferrato. In gypsum of Ukraine. “Escursione pre-Riunione: il sistema alpino Appenninico In the Moncalvo quarry, considering the volume of nel Cenozoico (6–9 settembre 2002)”, 81a Riunione the examined caves (about 10 000 m3) and the amount Estiva Società Geologica Italiana, Torino 10–12 settembre of the water flow in the inrush event (60 000 m3), other 2002, pp. 116–128. karst conduits are probably present above the actual Dela Pierre, F., Piana, F., Fioraso, G., Boano, P., Bicchi, E., groundwater table. At present, water in the quarry drifts Forno, M. G., Violanti, D., Balestro, G., Clari, P., is collected in proper basins and pumped outside the D’atri, A., De Luca, D., Morelli, M. & Ruffini, R. quarry in order to stabilize the groundwater table so 2003. Note Illustrative della Carta geologica d’Italia that the exploitation should continue in the higher alla scala 1 : 50.000; Foglio 157 Trino. Settore Studi e quarry panels. Quality evaluations of the mixing of ricerche Geologiche – Sistema Informativo Prevenzione different kinds of water inflows are necessary in order Rischi – ARPA, Litografia Geda, Nichelino, 2003, to establish proper use of the water on the basis of 147 pp. sulphate concentration and presence of pollutants. In Fornaro, M., Savasta, G., Accattino, G. & Amalberto, S. 1996. that case, due to the high values of TDS, electrical Progetto di una moderna coltivazione di gesso in conductivity, and sulphates, water is not suitable for sotterraneo ed inserimento ambientale dell’attività irrigation purposes and is reintroduced into the surface estrattiva. In IV Congresso Minerario Italo-brasiliano, drainage pattern. Canela (Brasile); EGATEA (no. especial), 104–114.

Fornaro, M., Innaurato, N., Mancini, R., Amalberto, S. & Pontarollo, J. N. 2000. Kammerauffahrung mit einer ACKNOWLEDGEMENT Teilschnittmaschine in einer Gipsgrube. In Proceedings of XXIV Symposium of the International Society for Rock Special thanks go to the company Fassa S.p.a. that owns Mechanics, Eurock 2000, pp. 501–506. Verlag Glückauf, the quarry in Molcalvo, for its contribution and consent Essen.

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Vajumisohust, mille on esile kutsunud karstialadel kaevandamine: Moncalvo kurisu sündmuse (Loode-Itaalias Piemontes) uus käsitlus

Sabrina Bonetto, Adriano Fiorucci, Mauro Fornaro ja Bartolomeo Vigna

Kips on oluline toormaterjal nii ehituses kui muudes tööstusharudes. Piemonte (Loode-Itaalias) peamised kipsi- lasundid paiknevad Monferrato piirkonnas, kus on ka suured karjäärid ja kaevandused. Seal paljandub kipsi sisaldav kihind, mis on tüüpilise geoloogilise, geostruktuurse ja hüdrogeoloogilise ehitusega, mõjustades nii kaevandamist kui ka suhteid seotud loodusnähtuste, inimtegevuse ning maakasutusega. Eriti tugevasti mõjustab kaevandamist kipsi- lasundi karstumus, nii nagu kaevetööd avaldavad olulist mõju ka kipsi karstumisele. On käsitletud spetsiifilist juhtumit, mis toimus Monferratos, kui kaevandamise, geoloogiliste ja hüdrogeoloogiliste tingimuste ning terri- toriaalse paiknemise koosmõju tulemusel tekkis pinnale ulatuv kurisu ja selle kaudu äkiline vee sissetung Moncalvo kaevandusse.

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